The present invention concerns a method and equipment for the production and maintenance of a gas mixture in one or more chambers, to be used mainly in connection with the treatment of animals and, in particular, for use in connection with poultry.
More specifically, the present invention is related to treatment such as stunning or killing poultry, and may expediently be used in connection with the applicant""s previous patent application PCT/N097/00331, which describes the use of gas mixtures containing mainly a constant, natural level of O2 concentration, whereby the concentration of CO2 may be varied in accordance with a further specified process during treatment. Such treatment may take place by varying the CO2 concentration continuously or in stages. Treatment in stages may preferably take place in three phases, which is, moreover, stated using examples in the above patent application.
In the following, a brief description will be given of how the gas treatment of poultry in three phases may take place:
Phase 1
This is an introductory phase in which the animals are made accustomed to an atmosphere which is different than a normal atmosphere. The purpose is to expose the animals to a low concentration of CO2 which causes no discomfort but which nevertheless appears to have a certain calming effect. It has been observed in many tests that this phase is decisive for how the animals react to the next phase. They behave very calmly in phase 2 if they have received the correct pretreatment, which is the purpose of phase 1. The dwell time in phase 1 is 30-40 seconds. Phase 1 may have the following atmosphere:
Phase 2
The actual stunning starts in this phase and the animals become completely relaxed and fall asleep. The atmosphere is changed further by the addition of more CO2. In this phase, the oxygen plays a very important role. If the oxygen concentration is too low, the animals become agitated with a lot of spasms. If the concentration is too high, however, it is more difficult to stun the animals. Our experience shows that the oxygen concentration should be close to that of a normal atmosphere. Dwell time is 40-50 seconds.
In this phase, the required CO2 concentration may vary beyond the recommended levels, depending on the type of animal and the size of the animals. The conditions must be regulated to meet individual requirements.
Phase 3
After phase 2, the animals are slightly stunned but will wake up again after a very short time. Phase 3 must therefore stun the animals more deeply so that it takes longer for them to wake up. The atmosphere is changed further by the addition of more CO2. The dwell time in phase 3 must be 30-40 seconds.
The required CO2 concentration may vary in this phase as well, depending on the type of animal and depending on whether the animals are to be stunned deeply or killed. Recently, we have also found out that the requirements for the quantity of O2 in this phase may be reduced down towards 10%, depending on the type of animal (for example, chicken) which is to be treated.
U.S. Pat. No. 5,653,629 relates to the slaughter of poultry in an oxygen-depleted atmosphere, in which the poultry is held in the atmosphere for a sufficient period of time to lose consciousness and then to die. The method is a one chamber method based upon stunning in an atmosphere with an extremely low oxygen concentration, such as less than 2% oxygen. In the examples, different compositions of atmospheres for batchwise treatment of the poultry are provided. In example 4, an oxygen concentration of 5% is indicated as being too high to achieve satisfactory stunning results. Further, no indications are given in the disclosure about how the desired atmosphere should be maintained during an industrial, continuous stunning process. In fact, this disclosure does not relate to the basic principles of the present application, where the poultry are exposed to a mainly normal level of oxygen. concentration during the stunning process, which in addition may involve plural atmospheres of treatment.
U.S. Pat. No. 5,152,714 is another example of anoxic poultry stunning where the gas mixture contains less than 2% oxygen.
The present invention is in particular suited for performance in relation to the principles given in the Applicant""s own patent application PCT/N097/00331, which is a non-oxygen depleted process for the treatment of poultry (i.e. the oxygen level is mainly at the natural level in the stunning gas mixtures). The treatment of animals with a gas mixture having a rather natural oxygen content is believed to be more humane than the prior art gas mixtures, because it is not a low level of oxygen that gives the stunning effect. It is rather the level of the carbon dioxide concentration that is the effective parameter in this sense.
WO 94/15469 relates to two-chamber stunning of poultry in which a stunning gas or gas mixture via a shut-off valve can be portioned to a mixing chamber. In addition, oxygen from a reservoir can be led to the same mixing chamber via another shut-off valve. Further, a portion of the gas can be transferred from one chamber to the other. This publication does not teach adding oxygen as a function of the carbon dioxide concentration measured in the gas from the zone(s), and also does not teach that the control of the oxygen addition can be of volumetric type. Further, it does not teach what the oxygen concentration should be in the second chamber.
The present invention describes a method and equipment for supplying and regulating the gas composition in the different phases of treatment. The present invention also ensures that it is easy to maintain the desired concentration in different zones of the stunning equipment in connection with treatment in stages and; on the other hand, to maintain the desired gas concentration during treatment by continuously changing the CO2, concentration. Moreover, the present invention contributes to the gas mixture/concentration being uniform throughout the zone (chamber/section) in which the animals are located during treatment. The above conditions are important parameters for achieving uniform quality of treatment of the animals so that all the animals are in the same state after treatment (stunned or killed). The treatment method has been specially developed with a view to reversible stunning, in which there are strict requirements for good control in connection with the gas mixtures in question if the animals are to be returned to their original state.